In-situ construction of porous Fe/Ni/Co-phosphide heterostructures with electron redistribution for the efficient water oxidation reaction

Abstract

Electrochemical water splitting efficiency is mainly limited by the kinetically sluggish and high overpotential oxygen evolution reaction (OER) at the anode, compared to the hydrogen evolution reaction (HER) at the cathode. Substantial efforts have been carried out to overcome the above limitations. In this work, highly active porous Fe/Ni/Co-phosphide heterostructures with electron redistribution and tailored porosity have been developed for OER catalysis application. The well-developed porosity is observed by HRTEM analysis, and the XPS analysis confirms the electronic charge redistribution. The as-synthesized catalyst exhibited an extremely low overpotential of 200 mV to reach a current density of 10 mA cm-2 and 215 mV at 50 mA cm-2 in 1 M KOH with a small Tafel slope of 42 mV dec- 1 benefiting from the synergistic advantages of active heterostructures together with porous nature and regulation of the electronic structure. Also, the catalyst showed steady longterm durability during the 35 h of continuous chronopotentiometry test. The catalyst showed a high faradic efficiency of 95.8%, measured by the Rotating Ring Disk Electrode (RRDE) experiment. RRDE experiment validates the evolution of oxygen from the water oxidation process. The post-TEM analysis of the catalysts suggests that the OER catalysis goes through the formation of active species like Ni(OH)2, NiOOH, FeOOH, and CoOOH. The formation of surface oxy-hydroxides and hydroxides is responsible for the excellent OER catalytic activity.